1. Field of the Invention
This invention relates to a sensitivity correcting method, a navigation system and a vehicle, and more particularly, is applied to a car navigation system for detecting the position of a vehicle and displaying its position on a map.
2. Description of the Related Art
Heretofore, various car navigation systems for reading out map data from the memory medium such as a compact disk read only memory (CD-ROM), and displaying a position of a vehicle on the map obtained to support the driver on his driving operation by guiding him along the road, have been provided. In such as car navigation system, a global positioning system (GPS) receiver has been widely used as a position detecting means for detecting the position of the vehicle. The GPS receiver receives positioning data from the plurality of satellites which rotate round the earth, and analyzes the positioning information to detect the position of the vehicle.
Since the GPS receiver basically detects the position by receiving radio waves from the GPS satellites, it causes a problem such as the position cannot be detected with sufficiently high accuracy when the vehicle is in an area like a city in which radio waves from the GPS satellites can hardly be received, or the vehicle is running at low speed.
To solve the above problem, various methods have been provided: One of them is a method of using a self-navigation system in addition to the GPS navigation described above. In the self-navigation system, the position of the vehicle is detected by obtaining a driving route of the vehicle based on a driving speed and running direction of the vehicle and adding the driving route to the coordinates at the start point of the vehicle. Therefore, in a car navigation system employing the GPS navigation and self-navigation systems, an angular velocity detector such as a piezo-electric vibrating gyroscope is provided. The running direction of the vehicle will be obtained by detecting its angular velocity when the vehicle changes the running direction. Note that, the driving speed is generally obtained from a speed detector provided in the vehicle.
In this manner, the latest car navigation system can accurately detect the position b vehicle by employing the GPS navigation to detect the position of which receiving radio waves from the GPS satellites, and the self-navigation to detect the position based on the driving speed and running direction (angular velocity) of the car.
In the self-navigation system, the position detection is performed on the basis of running directional data obtained by the angular velocity detector as described above. However, in general, the angular velocity detector has variations in its output sensitivity (that is the relationship between an angular velocity detected and the signal level of an output signal showing the angular velocity), thus it causes a problem that the running directional data obtained from the angular velocity detector varies so that an accurate position can not be detected.
To detect the correct position, the output sensitivity of the angular velocity detector is adjusted at the factory. However, the output sensitivity may vary again depending on the mounting manner of the car navigation to a vehicle. For example, in the case where an attachable position is limited, the car navigation system may be attached slanted, and thus the angular velocity detector is also slanted. As a result, the reference axis of rotating detection shifts from the desired direction (e.g., the perpendicular direction of the vehicle) and thus the expected output sensitivity can not be obtained.